Abstract
Modulation of cellular energy homeostasis is an attractive alternative to improve crop yield and plant performance under stressful conditions. Previously, we reported that overexpression of Arabidopsis NAD kinase2, which produces chloroplastic NADP, promoted nitrogen assimilation in Arabidopsis. Consequently, metabolites associated with the Calvin cycle were also accumulated. In this study, we generated transgenic plants overexpressing Arabidopsis NAD synthetase gene (NADS). NADS overexpressor plants did not show any remarkable changes in vegetative growth and the level of NAD(P)(H) was unexpectedly unchanged albeit enhanced NADS activity. However, NADS overexpression caused early ageing coincidentally with bolting. Then, the levels of NAD+ was drastically decreased and the levels of intermediates of NAD biosynthesis (NaMN and NaAD) and NAD derivatives (nicotinate and nicotinamide) were dramatically increased in NADS overexpressors after bolting. These results suggest that the levels of NAD(P)(H) could be kept properly during vegetative phase even under NADS overexpression and that bolting may act as a signal for the alteration of NAD homeostasis.
